The Russian double agent and the mystery substance: What we know so far

Here is what we know so far as Russian double agent Sergei Skripal and his daughter Yulia remain fighting for their lives in hospital after being exposed to a mystery substance.

- Mr Skripal, 66, was found along with his 33-year-old daughter on a bench in The Maltings in Salisbury, Wiltshire, after police were called by a concerned member of the public at around 4.15pm on Sunday.

- The pair, who did not have any visible injuries, were taken to Salisbury District Hospital, where they are being treated in intensive care for "suspected exposure to an unknown substance".

- Officers "secured" a number of scenes - including the Zizzi restaurant in Castle Street and the Bishop's Mill pub in The Maltings.

A police tent at the spot by The Maltings shopping centre where Sergei Skripal and his daughter were found (Andrew Matthews/PA)

- Mr Skripal was a double agent and was convicted in 2006 of passing state secrets to MI6 before being given refuge in the UK as part of a spy swap.

- He is a former colonel in Russian military intelligence, who was sentenced to 13 years in prison, and was among four convicts who were given pardons and one of two sent to Britain in 2010 in a deal that was said at the time to be the largest exchange since the Cold War.

- It is not being treated as a terrorist incident, but Scotland Yard said it is "keeping an open mind", and the probe is being led by the counter-terrorism policing network because of its "specialist expertise".

- It was revealed that a "small number" of emergency services personnel, including police, were assessed immediately after the incident, and all but one have been released from hospital.

Salisbury District Hospital (Steve Parsons/PA)

- Foreign Secretary Boris Johnson went on the offensive in the House of Commons about the "disturbing incident", noting that this case had "echoes" of the death of Alexander Litvinenko, a Russian dissident who was fatally poisoned in London in 2006.

- Mr Johnson also claimed Russia is "in many respects a malign and disruptive force".

- The Russian Embassy said it was "completely untrue" to suggest the country's special services were involved and criticised Mr Johnson for speaking "in such a manner as if the investigation was already over".

- The Defence Science and Technology Laboratory in Porton Down, Wiltshire, which has state-of-the-art equipment to look for trace amounts of substances, is believed to be involved in examining what could have caused Mr Skripal and his daughter to fall ill.

- The Government has called a meeting of its emergency committee Cobra on Wednesday morning, to be chaired by Home Secretary Amber Rudd.

- CCTV footage from a camera at Snap Fitness 24/7 gym emerged showing a man and a woman walking in the area moments before the pair were found.